Channelized rainscreen framework for construction of cementitious exterior walls

ABSTRACT

A channelized rainscreen framework for making a stucco wall by attaching a back side of the channelized rainscreen framework to a front side of a sheathing of a building and applying mortar to a front side of the channelized rainscreen framework. The channelized rainscreen framework comprising a lath sheet and a channel sheet, the channel sheet having a channel sheet front and a channel sheet back, the channel sheet front coupled to the lath sheet, the channel sheet having alternating troughs and peaks, the troughs and peaks running a length of the channel sheet, the peaks forward of the troughs, the channel sheet defining a plurality of channels behind the peaks. The channel sheet has a plurality of holes sized to allow enough mortar to penetrate through the channel sheet to embed it in the mortar, but not to fill the channels.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of, and priority to, U.S.Provisional Application No. 61886260 filed on 3 Oct. 2013, incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to building materials. More particularly,the present invention relates to building materials for constructingstucco walls.

BACKGROUND

Stucco as a wall cladding has been used for a long time. Until the1990s, a stucco wall was typically made by applying cementitiousmaterial over metal lath attached to building sheathing (typicallyplywood or strand board) with building paper as a water resistantbarrier in between. The cementitious material will shed some of thewater that is thrown on it by the weather, but some water will beabsorbed by the cementitious material and when the body of cementitiousmaterial is filled to its capacity, some moisture will sit on the insideof the cementitious material against the building sheathing. Also,moisture may be driven inwards through the cementitious material byvarious forces, including any difference in air pressure that may arisebetween the exterior of the wall and the inner layers. If there is asufficient gap between the cementitious material and the water resistantbarrier to form a wall cavity, the water will likely drain down and outof the wall. A small gap usually did occur between the cementitiousmaterial and older building papers that would allow some drainage. Evenso, this gap was not also sufficient to allow complete drainage due tosurface tension and unequalized pressure across the cementitiousmaterial.

Newer water resistant barrier materials, mostly plastics, have largelydisplaced the older paper materials. Regardless of the advantages ofplastic water resistant barrier materials, they had a disadvantage inthat they tended to bond to cementitious materials. With this tendency,no helpful gap appeared between the cementitious material and the waterresistant barrier. Water driven through the cementitious material wouldnot drain out, but would accumulate against the water resistant barrierand potentially be driven through it, where it would cause rot of thesheathing material.

The solution to this problem of water accumulation has been to create arainscreen by forming a cavity between the cementitious material and thewater resistant barrier. A rainscreen is defined as an exposed outerskin or surface element of a wall, backed by an air space. The cavitybehind the outer skin of the wall is typically created by placing adrainage mat between the cementitious material and the water resistantbarrier. Typical drainage mat include corrugated plastic sheets; dimpledplastic sheets; or mats of entangled plastic fibers. The drainage matpartially fills the cavity but has interior passages sufficiently largeenough for water to drain down and for air to circulate through.Circulating low humidity air from outside the wall into the wallinterior helps remove moisture from the back side of the cementitiousmaterial.

To function properly, the rainscreen should be pressure equalized, sothat a near zero-pressure difference exists at all times across therainscreen. A pressure-equalized rainscreen wall design aims to controlall forces that can drive water into the wall assembly—air pressuredifference, gravity, surface tension, capillary action, and rain dropmomentum. Of these, air pressure difference is usually the dominantforce with the potential to drive a considerable amount of water intothe wall assembly. To ensure adequate pressure equalization and aircirculation, the cavity behind the rainscreen must be vented to theexterior of the wall.

If cementitious material were applied directly to the typical drainagemat, the cementitious material would flow into the large interiorpassages in the drainage mat and block them, preventing drainage and airflow. To prevent this, an additional barrier layer—typically a sheet oftightly woven fabric or non-woven material—is placed between thedrainage mat and the cementitious material. This additional barrierincreases costs of construction and also slows drying of thecementitious material as it impedes the flow of moisture from the backside of the cementitious material into the cavity behind the rainscreenand prevents direct contact with the air circulating therein.

SUMMARY

Disclosed herein is an exemplary embodiment of a channelized rainscreenframework for making a stucco wall. The channelized rainscreen frameworkcomprises a lath sheet and a channel sheet. The channel sheet has achannel sheet front and a channel sheet back. The channel sheet front iscoupled to the lath sheet. The channel sheet has alternating troughs andpeaks, with the troughs and peaks running a length of the channel sheet,the peaks forward of the troughs, the channel sheet defining a pluralityof channels behind the peaks.

A back side of the channelized rainscreen framework is attached to afront side of a sheathing of a building. Then mortar is applied to afront side of the channelized rainscreen framework, filling a spacebetween the lath sheet and channel sheet with mortar, and covering thelath sheet with mortar. The channel sheet has a plurality of holes sizedto allow enough mortar to penetrate through the channel sheet to embedit in the mortar, but not to fill and block the channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a channelizedrainscreen framework rainscreen back.

FIG. 2 is a sectional view of an exterior wall assembly that includesthe channelized rainscreen framework of FIG. 1.

FIG. 3 is a detailed view of one of the channels of FIG. 2.

FIG. 4 is a detailed view of the channel sheet of FIG. 2, showing theinterface between the channel sheet and the sheathing.

FIG. 5 is a front view of the exterior wall assembly of FIG. 2.

DETAILED DESCRIPTION

Before beginning a detailed description of the subject invention,mention of the following is in order. When appropriate, like referencematerials and characters are used to designate identical, corresponding,or similar components in different figures. The figures associated withthis disclosure typically are not drawn with dimensional accuracy toscale, i.e., such drawings have been drafted with a focus on clarity ofviewing and understanding rather than dimensional accuracy.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application and business related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

Use of directional terms such as “upper,” “lower,” “above,” “below”, “infront of,” “behind,” etc. are intended to describe the positions and/ororientations of various components of the invention relative to oneanother as shown in the various Figures and are not intended to imposelimitations on any position and/or orientation of any embodiment of theinvention relative to any reference point external to the reference.

EXEMPLARY EMBODIMENT

FIG. 1 shows a perspective view of an embodiment of a channelizedrainscreen framework 100. The channelized rainscreen framework 100 isdesigned for use in constructing mortar-based (e.g. stucco or stonefaçade) exterior wall envelopes that are weather-resistant and provide ameans for draining water that enters the exterior wall. The channelizedrainscreen framework 100 comprises a lath sheet 102 coupled to a channelsheet 104, with the lath sheet 102 on the front side of the channelizedrainscreen framework 100 and the channel sheet 104 on the back side. Inthe exemplary embodiment, the lath sheet 102 is coupled to the channelsheet 104 with glue, but in other embodiments may be coupled in otherways such as heat bonding or mechanical fasteners. The channelizedrainscreen framework 100 is designed to be attached to a building withits backside (i.e., the side with the channel sheet 104) toward thebuilding. Mortar or other cementitious material is then applied to thefront side (i.e., the side with the lath sheet 102), filling the spacebetween the lath sheet 102 and channel sheet 104 and covering the lathsheet 102. (See FIG. 2).

The lath sheet 102 is a sheet of material designed to support stucco,mortar or other cementitious material. In the exemplary embodiment, thelath sheet 102 comprises a mesh of lath strands, specifically fiberglass strands, but in other embodiments may be comprised of othersuitable materials such as metal, basalt or any composite material.

The channel sheet 104 is shaped with alternating troughs and peaksrunning down a length of the sheet. The troughs 106 are closer to theback of the channelized rainscreen framework 100 and the peaks 108 arecloser to the front. The lath sheet 102 is attached to the front sidesof the peaks 108. The boundary between one of the peaks 108 and one ofthe troughs 106 adjacent to it is a point on the channel sheet 104 thatis half way between a farthest forward point on the peak 108 and thefarthest rearward point of the trough 106. In the exemplary embodiment,the channel sheet 104 has a trapezoidal profile, with flat portions atthe peaks 108, troughs 106 with flat portions wider than the flatportions of the peaks 108 and fairly sharp transitions between the peaks108 and troughs 106. Other embodiments may have other profiles forchannel sheet 104. For example, the profile of the channel sheet 104 maybe sinusoid with rounded peaks 108 and troughs 106, or have peaks 108and troughs 106 that are sharp angled, or may have peaks 108 and troughs106 that are a combination of sharp angle, rounded, and/or flat.

Channels 120 are defined in the region behind the peaks 108 of thechannel sheet 104. The boundaries of one of the channels 120 are thechannel sheet 104 and a plane intersecting the rearward-most points onone of the troughs 106 adjacent to the channel 120. The channel 120provides a path for air to circulate and for water to drain out behindthe exterior wall (rainscreen) created when mortar is applied to thechannelized rainscreen framework 100.

The channel sheet 104 comprises a sheet of entangled filaments. In theexemplary embodiment, the channel sheet 104 comprises filaments ofPolypropylene, but in other embodiments, may comprise filaments of othersuitable materials such as nylon. The entangled filaments are numerous,thick and dense enough to almost form a solid sheet, but still leave alarge number of holes 134 that penetrate the channel sheet 104. Thesizes of the holes 134 vary, because the process of depositing thefilaments in a sheet is random. However, the average hole size can becontrolled by the mass of filament material deposited per unit area ofthe sheet. For example, an increased filament material mass per unitarea results in a decreased average hole size. Maximum hole size can becontrolled by inspection and discarding of sheets exceeding a selectedmaximum.

The size of the holes 134 in the channel sheet 104 is a significantfactor in controlling the flow of mortar applied to the channelizedrainscreen framework 100. The channelized rainscreen framework 100 isdesigned to have mortar applied from the front side, filling the spacebetween the lath sheet 102 and channel sheet 104 and covering the lathsheet 102. The channel sheet 104 is made with holes 134 with an averagesize sufficiently small so that when typical mortar is applied to thefilament sheet front with pressures typically used in mortarapplication, the mortar will protrude beyond the back of the channelsheet 104 some distance, enough to embed the channel sheet 104 in themortar, but not enough to fill and block the channels 120. In theexemplary embodiment, the filament material mass per unit area depositedis in the range of 5 to 15 ounces per square yard and maximum hole sizeis limited to 0.25 inches with most holes smaller than 0.25 inches. Thisgives good results with mortars typically used in the building industry,allowing some mortar to protrude behind the channel sheet 104 but notenough to block the channels 120. However, channel sheets 104 with otherranges of filament material mass per unit area and hole sizes may beused in other embodiments.

Any point on the lath sheet 102 has a filament sheet depth that isdefined as the shortest distance between the lath sheet 102 and thechannel sheet 104. The channelized rainscreen framework 100 has a designfraction that is defined as the fraction of points on the lath sheet 102that have a filament sheet depth that is at least the design filamentsheet depth. The design filament sheet depth is based on building coderequirements for a depth to which lath must be embedded in mortar andthe design fraction is based on a building code requirement for theamount of lath that must be embedded in mortar. In the exemplaryembodiment, the channelized rainscreen framework 100 is constructed tohave a design filament sheet depth of 0.25 inches and a design fractionof at least 50%. This is because current US building codes require atleast 50% of the lath to be embedded in mortar by at least 0.25 inches.However, in other countries the building codes may differ and buildingcodes may change in time, so other embodiments may have different designfilament sheet depths and design fractions.

In the exemplary embodiment, the channel sheet 104 has a trapezoidalprofile with sharp transitions between peaks 108 and troughs 106. Theflat portions of the peaks 108 are 0.25 inches wide and have 1 inch gapsbetween them. The flat portions of the troughs 106 are 0.75 inches wideand have 0.5 inch gaps between them. Other embodiments may have otherprofiles and other dimensions for the peaks 108 and troughs 106.

FIG. 2 shows a sectional view of an exterior wall assembly 128 thatincludes the channelized rainscreen framework 100 of FIG. 1. Thechannelized rainscreen framework 100 is attached to a sheathing 118 of abuilding with a plurality of fasteners 110. Preferably, a waterresistant barrier 116 is attached to the sheathing 118 between the frontside of the sheathing 118 and the back side of the channel sheet 104.Mortar applied to the front of the channelized rainscreen framework 100forms an inner mortar layer 132 in the region between the lath sheet 102and the channel sheet 104 and forms an outer mortar layer 130 in frontof the lath sheet 102. This application of mortar also forms mortarprotrusions 114 into the channel sheet 104 and in some instances,through and into the channels 120 behind the channel sheet 104.

FIG. 3 shows a detailed view of one of the channels 120 of FIG. 2,showing the mortar protrusions 114 in greater detail. The mortarprotrusions 114 that penetrate through the channel sheet 104 and intothe channels 120 provide several advantages. One advantage is that thesemortar protrusions 114 provide additional surface area for waterremoval. Low humidity air in the channels 120 draw out water directlyinto vapor. The mortar protrusions 114 provide additional surface areaaffording more contact between air and cementitious material,accelerating water removal. When the interior part of the cementitiousmaterial facing the channels 120 dries, water then migrates frominterior parts of the cementitious material and in turn is removed.Another advantage that mortar protrusions 114 provide is the disruptionof surface tension. When water is driven into the cementitious material,some moisture will weep out the back side into the channels 120. Whensufficient water weeps out in a localized spot, a drop forms, but clingsto the wall of the channel 120, held in place by surface tension. Thedrop grows larger until gravity overcomes the surface tension holdingthe drop to the wall of the channel 120, causing the drop of water toflow down the channel 120. While the drop is clinging to the sides ofthe channel 120, migration of water out of the cementitious material isslowed. The irregular shapes of the mortar protrusions 114 disrupt thesurface tension of forming drops, causing them to flow away sooner at asmaller size, thereby accelerating the drying of the cementitiousmaterial.

FIG. 4 is a detailed view of the channel sheet 104 of FIG. 2, showingthe interface between the channel sheet 104 and the sheathing 118. Thisapplication of mortar also forms mortar protrusions 114 into the channelsheet 104, but in areas where the channel sheet 104 is adjacent thesheathing 118, the mortar protrusions 114 do not extend through thechannel sheet 104 and typically do not extend very far into the channelsheet 104. This happens because when mortar is applied to thechannelized rainscreen framework 100, the pressure applied istransmitted through the mortar to the channel sheet 104, compressing itagainst the sheathing 118 and compressing any air or water trappedbetween. This compression creates a back force that works to keep themortar out of the channel sheet 104. Additional, in the exemplaryembodiment, the flat portions of the troughs 106 of the channel sheet104 adjacent the sheathing 118 are denser in filament material than theareas bordering the channels 120. This results in the flat portions ofthe troughs 106 having holes with a smaller average size than in theportions of the channel sheet 104 adjacent the channels 120. Smalleraverage hole size will decrease the average depth of mortar penetrationinto the channel sheet 104. Since mortar does not penetrate much intothe channel sheet 104 in the flat portions of the troughs 106, water 126and air can flow in the cavity space between the inner mortar layer 132and the sheathing 118.

Higher filament density in the flat portions of the troughs 106 may be aresult of deliberate efforts to deposit more filament material in theflat portions of the troughs 106 of the channel sheet 104, or may be anincidental result a simple way of making the channel sheet 104—droppingfilament material evenly over a horizontally oriented form for thechannel sheet 104. If the form has the desired profile for the channelsheet 104, dropping filament material evenly over the form willnaturally result in more material being deposited on horizontal surfacessuch as those in the flat portions of the troughs 106 and less on thenon-horizontal surface.

FIG. 5 shows a front view of the exterior wall assembly 128 of FIG. 2.The exterior wall assembly 128 has a vent 122 at the top and an exhaust124 at the bottom. The vent 122 and exhaust 124 penetrate throughchannelized rainscreen framework 100, the outer mortar layer 130 andinner mortar layer 132 to connect with the channels 120 to create apressure equalized wall that will maintain near zero pressuredifferential between the space in front of the exterior wall assembly128 and the channels 120. This will reduce the driving of water throughthe outer mortar layer 130 to the inner mortar layer 132. Air cancirculate from the outside through the channels 120, removing water inthe form of vapor from the inner mortar layer 132. Water 126 in liquidform drains down the channels 120 and out the bottom of the exteriorwall assembly 128 through the exhaust 124. The vent 122 and exhaust 124are configured so that air may enter easily, but rain, especiallywind-driven drain cannot enter easily. To accomplish this, the vent 122and exhaust 124 passage through the exterior wall are typically angledupwards from outside to inside.

It is well known that to adequately relieve dynamic pressure (i.e.,pressure that fluctuates quickly with time and location, typicallycaused by wind), the ratio of the venting area to the volume of thecavity behind the rainscreen must be sufficiently large, so that changesin dynamic pressure due to wind gusts can be quickly relieved. Comparedto prior designs with a drainage mat or similar structure, the exteriorwall assembly 128 using the channelized rainscreen framework 100described herein has a smaller cavity volume, which allows the ventingarea to be smaller. That is, the vent 122 and exhaust 124 may besmaller.

Dynamic pressure on a building façade varies not only with time, butalso with its location on the façade. This spatial variation in pressurecan induce lateral airflow within the cavity. Standards bodies, such asthe National Research Council of Canada recommend dividing the cavitybehind the rainscreen at suitable intervals with delimiters that aresomewhat impervious to air and properly connected to the rainscreen andto the water resistant/air resistant barrier on the building sheath. Thecompartmentation of the cavity into smaller air compartments reduces therange of dynamic pressures sustained by each of these compartments,resulting in a better potential for pressure equalization across therainscreen. Typically, these delimiters are added in with additionalmaterials, such as metal flashing. In the exterior wall assembly 128using the channelized rainscreen framework 100 described hereinseparates the cavity behind the rainscreen into channels 120 delimitedby the inner mortar layer 132 and the channel sheet 104. As noted abovein the discussion of FIG. 4, air can flow through the channel sheetbetween the inner mortar layer 132 and the sheathing 118, but the gap issmall enough that not much lateral airflow is induced. Thus standardsfor compartmentation of the cavity behind the rainscreen can be metinherently using the channelized rainscreen framework 100 withoutadditional engineering or materials.

Many prior art designs would omit the vent at the top of the wall andonly have an exhaust on the bottom of the wall due to concerns aboutdynamic pressure which would require compartmentalization and vents notjust at the top of the wall, but at the top of each compartment as well.This is undesirable from an aesthetic point of view, but primarilyundesirable practically as more vents, especially at mid-points up thewall give increase chances for wind-blown rain to get inside therainscreen. However, omitting the upper vent forgoes the advantage ofincreased circulation of air through the cavity. The channels 120 thatresult from using the channelized rainscreen framework 100 are small andnarrow, allowing venting standards to be met, but with the vents 122 andexhaust 124 more widely separated than in typical prior designs,allowing the vents 122 to be left in and the advantages of aircirculation to be gained.

Those skilled in the art will recognize that numerous modifications andchanges may be made to the exemplary embodiment without departing fromthe scope of the claimed invention. It will, of course, be understoodthat modifications of the invention, in its various aspects, will beapparent to those skilled in the art, some being apparent only afterstudy, others being matters of routine mechanical, chemical andelectronic design. No single feature, function or property of theexemplary embodiment is essential. Other embodiments are possible, theirspecific designs depending upon the particular application. As such, thescope of the invention should not be limited by the particularembodiments herein described but should be defined only by the appendedclaims and equivalents thereof.

What is claimed is:
 1. An article of manufacture comprising; a lathsheet; a channel sheet with a channel sheet front and a channel sheetback, the channel sheet front coupled to the lath sheet, the channelsheet having alternating troughs and peaks, the troughs and peaksrunning a length of the channel sheet, the peaks forward of the troughs,the channel sheet defining a plurality of channels behind the peaks; andwherein the channel sheet has a plurality of holes having a typical sizesufficiently small enough that when mortar is applied to the channelsheet front under typical installation pressure, the mortar will notprotrude through the channel sheet enough to block the channels.
 2. Thearticle of manufacture of claim 1, wherein any point on the lath has achannel sheet depth that is a shortest distance between that point andthe channel sheet; and wherein the article of manufacture has a designfraction that is a fraction of points on the lath that have a channelsheet depth that is at least a design channel sheet depth.
 3. Thearticle of manufacture of claim 2, wherein the design channel sheetdepth is based on a building code requirement for a depth to which lathmust be embedded in mortar; and wherein the design fraction is based ona building code requirement for an amount of lath that must be embeddedin mortar.
 4. The article of manufacture of claim 3, wherein the designchannel sheet depth is 0.25 inches and the design fraction is 50%. 5.The article of manufacture of claim 1, mortar substantially covering thelath and substantially filling a space between the lath and the channelsheet.
 6. The article of manufacture of claim 5, wherein the mortarprotrudes slightly beyond the channel sheet creating mortar protrusionsinto the channels.
 7. The article of manufacture of claim 1, furthercomprising: wherein the channel sheet has a trapezoidal profile.
 8. Thearticle of manufacture of claim 1, wherein the channel sheet has asinusoidal profile.
 9. The article of manufacture of claim 1, whereinthe channel sheet comprising entangled filaments.
 10. The article ofmanufacture of claim 9, wherein the channel sheet weighs at least 5ounces per square yard and n than 15 ounces per square yard.
 11. Thearticle of manufacture of claim 1, wherein the holes in the channelsheet adjacent the channels have a larger average size than in otherportions of the channel sheet.
 12. An exterior wall assembly comprising;a sheathing of a building; a channelized rainscreen framework coupled toa front side of the sheathing, the channelized rainscreen frameworkcomprising a lath sheet and a channel sheet, the channel sheet having achannel sheet front and a channel sheet back, the channel sheet frontcoupled to the lath sheet, the channel sheet having alternating troughsand peaks, the troughs and peaks running a length of the channel sheet,the peaks forward of the troughs, the channel sheet defining a pluralityof channels behind the peaks, wherein the channel sheet has a pluralityof holes; an outer mortar layer in front of the lath sheet; and an innermortar layer in a region between the lath sheet and the channel sheet.13. The exterior wall assembly of claim 12, wherein the plurality ofchannels run vertically on the building, providing an open passage forwater to drain down between the sheathing and the channel sheet.
 14. Theexterior wall assembly of claim 12, wherein the inner mortar layer hasprotrusion that pass through the plurality of holes in the channel sheetand into the channel.
 15. The exterior wall assembly of claim 12,wherein any point on the lath has a channel sheet depth that is ashortest distance between that point and the channel sheet; and whereinchannelized rainscreen framework has a design fraction that is afraction of points on the lath that have a channel sheet depth that isat least a design channel sheet depth.
 16. The exterior wall assembly ofclaim 15, wherein exterior wall assembly of claim 12, the design channelsheet depth is based on a building code requirement for a depth to whichlath must be embedded in mortar; and wherein the design fraction isbased on a building code requirement for an amount of lath that must beembedded in mortar.
 17. A method for making a stucco wall comprising thesteps of; providing a channelized rainscreen framework comprising a lathsheet and a channel sheet, the channel sheet having a channel sheetfront and a channel sheet back, the channel sheet front coupled to thelath sheet, the channel sheet having alternating troughs and peaks, thetroughs and peaks running a length of the channel sheet, the peaksforward of the troughs, the channel sheet defining a plurality ofchannels behind the peaks, wherein the channel sheet has a plurality ofholes; attaching a back side of the channelized rainscreen framework toa front side of a sheathing of a building; and applying mortar to the afront side of the channelized rainscreen framework.
 18. The method ofclaim 17, wherein the step of apply mortar further comprises the stepsof: filling a space between the lath sheet and channel sheet withmortar; and covering the lath sheet with mortar.